LM2707 Datasheet, PDF (1/19 Pages) National Semiconductor (TI) – Inductive-Boost Series LED Driver with Programmable Oscillator Frequency

February 2005
LM2707
Inductive-Boost Series LED Driver with Programmable
Oscillator Frequency
General Description
The LM2707 is a magnetic boost regulator specifically de-
signed for white LED drive applications. Tightly regulated
LED currents, exceptional LED brightness uniformity, and
very high LED-drive power efficiency (>80%) can all be
achieved by stacking the LEDs in series between the
LM2707 output and the low-voltage feedback pin (0.515V).
The LM2707 requires only a few small external components.
A small inductor with a low saturation current rating can
safely be used because the tightly controlled current limit
circuit prevents large inductor current spikes, even at start-
up. The output capacitor can also be small due to the tightly
controlled output over-voltage protection circuit.
The LM2707 is an excellent choice for display backlighting
and other general-purpose lighting functions in battery pow-
ered applications. The 2.3V-to-7V input voltage range of the
device easily accommodates single-cell Lithium-Ion batter-
ies and battery chargers.
The LM2707 features 18V output capability, PFM regulation,
and a high-current switching transistor (400mA peak). These
characteristics allow the part to drive a series string of 2-to-4
LEDs with forward currents between 0 and 40mA. LED
brightness can be adjusted dynamically simply by applying a
PWM signal to the enable (EN) pin. The PWM signal can be
as fast as 50kHz because the LM2707 has a fast turn-on
time.
In addition to LED-drive applications, the LM2707 can also
be used as a general purpose DC-DC voltage regulator in
boost converter applications.
The LM2707 is available in a SOT23-8 surface mount pack-
age.
Features
n Excellent LED Drive Capability:
3 LED String: 30mA
4 LED String: 20 mA
6 LEDs (2 strings of 3): 15 mA
n Very High LED Drive Efficiency: > 80%
n Low Feedback Voltage: 515mV
n Low-Resistance NMOS Power Switch: 0.6Ω
n High-Speed PWM Brightness Control Capability
n Over-Voltage Protection (18V min, 19V typ, 20V max)
n Inrush and Inductor Current Limiting
n 2.3V - 7V Input Voltage Range
n Requires Only a Few External Components
n No External Compensation Needed
n Programmable Oscillator Frequency
n ON/OFF Pin
n Small SOT23-8 Package
Applications
n White LED Drive for Display Backlights
n LED Flashlights
n General Purpose LED Lighting
n Step-up DC/DC Voltage Conversion
Typical Application Circuit
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